1. Field of the Invention
The present invention relates to a vehicle air conditioning system that controls compressor cycling in order to reduce engine workload. More specifically, the present invention relates to a vehicle air conditioning system that controls compressor cycling in response to humidity conditions at the air conditioning system evaporator.
2. Background Information
Vehicle air conditioning systems typically maintain the temperature of the passenger compartment by operating a compressor to keep the evaporator at a temperature just above the freezing point of water. Air passing through the evaporator is cooled but is too cold to send directly into the passenger compartment. In recent model vehicles, a portion of the cooled air is re-heated by passing the portion of the cooled air through the heater core. The cold air and the re-heated air are mixed together prior to entering the passenger compartment in order to deliver cooled air that is not frigid.
This conventional way of operating the vehicle air conditioning system is inherently inefficient. Energy is wasted by cooling the evaporator to a temperature just above the freezing point of water regardless of the cooling requirements. Further, the re-heating of cooled air represents an additional waste of energy.
Further, since the evaporator is cooled to a temperature that is close to, but above the freezing point of water regardless of cooling requirements of the air conditioning system, the cooled air is substantially dehumidified. Specifically, the majority of the moisture in the air passing through the evaporator condenses on the outer cooling surfaces of the evaporator. This moisture then typically drains out of the evaporator casing and falls beneath the vehicle. This results in an over-drying of the air entering the passenger compartment. For the comfort of the passengers, it is not necessary to remove all the moisture from the cooled air.
From a safety perspective, it is only necessary to remove sufficient amounts of moisture from the cooled air to prevent fogging on the interior surfaces of the windows of the vehicle. From a comfort perspective, it is only necessary to remove sufficient amounts of moisture to make passengers feel cool and comfortable.
Another disadvantage to the above air conditioner operation relates to odor management. Specifically, when the passenger compartment reaches the requested temperature, the compressor may shut off for a lengthy period of time before operating again. Under such circumstances, if the blower is still blowing air through the evaporator, moisture that has collected on the evaporator begins to evaporate. The vaporized moisture can have an undesirable aroma as it enters the passenger compartment.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved vehicle air conditioning system that operates in a more efficient manner and reduces formation of undesirable odors. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.